Method of condensing petroleum fractions



y 1935. a. B. COUBROUGH 2,002,731

METHOD OF CONDENSING PETROLEUM FRACTIONS Filed March 20, 1933 Patented May 28, 1935 UNITED STATES PATENT OFFICE METHOD OF CONDENSING PETROLEUM FRACTIONS Application March 20, 1933, Serial No. 661,727

1 Claim.

The present invention relates to condensation of high boiling petroleum fractions under vacuum.

In the vacuum distillation of heavy petroleum fractions, the maintenance of vacuum is primarily dependent on substantially complete condensation of the vapors. Although the purpose of vacuum operation is to reduce the vaporizing temperature, the distillation of the heaviest fraction can rarely be accomplished without exceeding the cracking temperature. Accordingly, there is usually present some cracked distillate in the vapors. This cracked distillate consists of low boiling hydrocarbons which are non-condensable under vacuum and as a result, must be handled as a non-condensable gas by the air pump. Since the air pump is designed only to exhaust air from the system, it becomes overloaded and thereby causes a decrease in the vacuum, with consequent necessity of further heating and increased evolution of low boiling cracked vapors.

According to the present invention, the vapors, after being subjected to condensation in any suitable manner, are contacted with a cooled oil in a direct contact condenser, the oil used as the contact medium being one which has no appreciable vapor pressure at the existing tempera:

ture. This oil acts as a solvent for the cracked vapors and removes them by absorption even though the temperature may be higher than the actual condensing temperature of the vapors. The removal of the cracked vapors relieves the duty on the air pump and permits it to perform its primary function of exhausting the air.

The accompanying drawing is a diagram of the preferred form of apparatus for practising the present invention.

The apparatus shown in the drawing comprises a column 2, only the upper part of which is illustrated. The column contains vapors of heavy lubricating fractions which are distilled in the bottom of the column in any suitable manner. The vapors pass through a vapor pipe 4 to a surface condenser 6 of any suitable form. Cooling water is circulated through the condenser by inlet and outlet pipes 8 and I0 respectively. The condensate is withdrawn from the condenser E by the pipe l2 and a portion is introduced into the column as reflux at M, the remainder being withdrawn as a product.

Any vapors remaining uncondensed pass from the condenser 6 to the barometric condenser 16, in which they are contacted directly with water introduced through the pipe I8. The mixed condensate and water are conducted through the barometric leg l9 to a suitable separator. This condensation effectively liquefies any light vapors, except cracked vapors non-condensable at available cooling water temperatures.

The remnant of vapors consisting of non-condensable cracked distillate and air pass from the barometric condenser l6 through a pipe 20 to an absorber 22. Into this absorber is introduced a cooled heavy oil by a pipe 24. The oil preferably comprises a heavy gas oil which has a marked absorbing power for the cracked vapors and which is itself uuvaporizable at the temperature existing in the absorber 22. This temperaturewill be somewhat higher than the temperature of the cooling water used in the condenser 6. The absorber 22 is provided with any suitable baffles or contact means 23 to promote intimate contact between the vapors and the oil. The oil with the absorbed cracked vapors is passed through a pipe 26 to a surge tank of any suitable form.

From the absorber 22, a pipe 28 leads to the air pump 30 which is illustrated as the conventional steam jets. Steam is admitted through a pipe 32. Since the heavy oil vapors have been previously condensed in the condenser 6 and the barometric condenser l6, and the cracked vapors have been removed in the absorber 22, the steam jet is called upon to perform only its intended function of pumping air from the system. As a result, the steam jet may be of minimum size and therefore requires only a small quantity of steam for its operation. The water condensed in the apparatus is conducted by a pipe 34 to the barometric leg l9 and is then conducted to the separator.

Having thus described the invention, what is claimed is:

A method of condensing under vacuum hydrocarbon vapors containing some low boiling cracked distillate vapors which consists in first liquefying uncracked vapors by surface condensation, contacting the uncondensed vapors directly with water, absorbing the non-condensable cracked vapors in a heavy hydrocarbon having a negligible vapor pressure, and pumping air from the system.

GEORGE E. COUZBROUGH. 

